Automatic reverse channel assignment in a two-way TDM communication system

ABSTRACT

To minimize overhead in the allocation of channels, forward and reverse link time slots are automatically assigned in pairs. In particular, rather than requiring a separate process for allocating reverse link channels for the sending of acknowledgment messages in response to receipt of a forward link packet, a different scenario takes place. At the receiving end, such as for valid reception of data on a forward link channel at a central base station site, a reverse link time slot is automatically allocated in a time slot which depends upon the time slot allocation on the forward link. This assists with the rapid return of acknowledgment messages in a reverse link direction which is the predominant direction for such messages in a wireless system wherein most data traffic is Web page oriented.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.09/574,622, filed May 19, 2000, now U.S. Pat. No. 6,804,252 the entireteachings of which are incorporated herein by reference.

BACKGROUND

Continued growth in the electronics and computer industries, and indeedin the economy in general, is increasingly driven by the demand foraccess to the Internet and the myriad of services and features that itprovides. The proliferation in the use of portable computing equipment,such as laptop computers, hand-held Personal Digital Assistants (PDAs)and Internet-enabled cellular telephones have resulted in acorresponding increase in demand for wireless access to computernetworks. However, at the present time, existing wireless networks, suchas the cellular telephone network, are not optimum for datacommunications. This is at least in part due to the architecture of suchnetworks as originally designed. In particular, these networks wereintended to support voice communications, as compared to the digitalcommunication protocols needed for Internet packet-orientedcommunications. For example, voice grade services typically requireaccess to a communication channel bandwidth of approximately 3 kilohertz(kHz). While techniques do exist for communicating data over such radiochannels at a rate of 9.6 kilobits per second (kbps), such low bandwidthchannels do not lend themselves directly to efficient transmission ofdata at the typical rates of 56.6 kbps or higher that are now commonlyexpected using wireless modems.

In addition, the very nature of Internet traffic itself is differentfrom the nature of voice traffic. Voice communication requires acontinuous duplex connection, that is, a user at one end of a connectionexpects to be able to transmit and receive to a user at the other end ofa connection, while at the same the user at the other end is alsotransmitting and receiving.

However, the usage patterns of Internet data transmission systems arequite different from voice. For example, consider that access to Webpages over the Internet in general is burst-oriented. Typically, theuser of a remote client computer first specifies the address of a Webpage to a browser program. The browser program at the client computerthen sends the request as a Transmission Control Protocol (TCP)/InternetProtocol (IP) message packet, which is typically about 100 bytes inlength, to a network Web server. The Web server then responds with thecontent of the requested Web page, which may include anywhere fromapproximately 10 kilobytes to several megabytes of text, image, audio orvideo data. The user may thereafter spend several seconds or evenseveral minutes reading the contents of the page before specifying anext Web page to be downloaded.

The result is that a typical Internet connection remains idle for arelatively long period of time. However, once a request is made, theuser expects the information to be transmitted to the client at arelatively rapid rate. Therefore, making available channels only on aninstantaneous “as needed” basis makes sense and indeed is a requirementif wireless data transfer services are to efficiently co-exist with theexisting wireless voice communication systems. Therefore, dynamictraffic channel allocation schemes are required to increase theefficiency of high performance wireless data communication systems in aneffort to more efficiently utilize available channel resources.

Furthermore, in most wireless systems, there are typically many morepotential users or subscribers than available radio channel resources.Therefore, some type of demand-based multiple access technique istherefore typically required to make maximum use of the available radiochannels. Multiple access is often provided in the physical layer, suchas by Frequency Division Multiple Access (FDMA) or by schemes thatmanipulate the radio frequency signal such as Time Division MultipleAccess (TDMA) or Code Division Multiple Access (CDMA). In any event, thenature of the radio spectrum is such that it is a medium that isexpected to be shared. This is quite dissimilar to the traditionalenvironment for data transmission, in which a wired medium such as atelephone line or network cabling is relatively inexpensive to obtainand to keep open all the time.

SUMMARY OF THE INVENTION

A particular problem exists with efficiently adapting communicationsystems which use on-demand multiple access techniques in the physicallayer to efficiently handle the TCP/IP message traffic which isprevalent in Internet communications. Consider that the TCP/IP protocolis a frame-based protocol requiring the acknowledgment of the receipt ofmessage frames. Thus, for example, when a user requests that a Web pagebe transmitted, the initial message requesting the Web page is sent on areverse link communication channel from a client computer towards a Webserver computer. The sending of the request message also requiresallocation of a forward link connection to allow the acknowledgmentmessage to return from the server to the client.

Unfortunately, in a wireless communication environment in which demandaccess is granted to wireless radio channels, opening up a new reverselink channel for the acknowledgment message is a time consuming process.For example, to allocate a channel in the reverse link direction mayindeed end up taking longer than the time necessary to simply transmitthe very short acknowledgment message.

The present invention seeks to overcome these difficulties. Theinvention is used in a time division multiplex (TDM) communicationsystem supporting duplex operations whereby multiple users share forwardand reverse channels. The system makes use of time slots to allocatespecific channels on a demand basis. Thus, for example, a given forwardlink channel is allocated for only a predetermined time slot durationand only upon user request.

To minimize overhead in the allocation of channels, forward and reverselink time slots are automatically assigned in pairs. In particular,rather than requiring a separate process for allocating reverse linkchannels for the sending of acknowledgment messages in response toreceipt of a forward link packet, a different scenario takes place. Atthe receiving end, such as for valid reception of data on a forward linkchannel at a central base station site, a reverse link time slot isautomatically allocated in a time slot which depends upon the time slotallocation on the forward link.

This scheme assists with the rapid return of acknowledgment messages ina reverse link direction which is the predominant direction for suchmessages in a wireless system wherein most data traffic is Web pageoriented.

The invention has several other advantages. Among these include theavoidance of the need to set up and tear down channels, especiallyreverse link channels, for the limited purpose of sending acknowledgmentmessages.

Minimizing the amount of reverse link traffic on shared frequencychannels, such as in a CDMA system, in turn increases the data handlingcapacity of the entire system. The reverse link messages may alsoinclude other types of anticipated short messages, depending upon thetype of forward link messages sent. For example, these may include linklayer acknowledgment messages, or higher layer GET messages for linksembedded in a Web page.

While the invention provides particular advantages in not explicitlyallocating reverse link traffic channels for the anticipation ofacknowledgment and other short messages, dedicated reverse link channelsmay still be explicitly allocated for long message traffic.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a block diagram of a communication system in which reversechannel assignment occurs automatically in response to valid receptionof data on a forward link channel.

FIG. 2 is a diagram depicting channel slot assignments.

FIG. 3 is a message sequence chart illustrating a typical message senton the reverse link and the resulting acknowledgment sent on the forwardlink.

FIG. 4 is a message sequence chart illustrating a typical forward linkmessage and resulting acknowledgment message to sequence on the reverselink.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 is a block diagram of a communication system 10 that is suitablefor automatic assignment of a reverse link channel such as to carryacknowledgment messages in response to a receipt of a valid message on aforward link channel. In particular, the communication system 10 shownincludes a number of personal computer (PC) devices 12-1, 12-2, . . .12-h, . . . 12-1, and corresponding Subscriber Access Units (SAUs) 14-1,14-2, . . . 14-h, . . . 14-1, and associated antennas 16-1, 16-2, . . .16-h, . . . 16-1. Centrally located equipment includes a base stationantenna 18, a base station processor (BSP) 20, Internet gateway 22,Internet 24, and network file server 30. The system is a demand access,point to multi-point wireless communication system such that the PCs 12may transmit data to and receive data from network server 30 throughwireless connections implemented over forward links 40 and reverse links50. It should be understood that in a point to multi-point multipleaccess wireless communication system 10 as shown, a given base stationprocessor 20 typically supports communication with a number of differentsubscriber access units 14 in a manner which is similar to that used ina cellular telephone communication network.

The PCs 12 may, for example, be laptop computers 12-1, handheld 12-h, orPersonal Digital Assistant (PDA)-type computers. The computers 12 areeach connected to a respective SAU 14 through a suitable wiredconnection such as an Ethernet-type connection. The respective SAU 14permits the PC 12 to be connected to the network file server 30 throughseveral types of physical connections.

In the reverse link direction, that is, for data traffic traveling fromthe PC 12 towards the server 30, the PC 12 provides an Internet Protocol(IP) level packet to the SAU 14 over the wired connection. The SAU 14then appends to the wired framing (i.e., Ethernet framing) in the IPpacket and inserts appropriate wireless connection framing. Theappropriately formatted wireless data packet then travels over one ormore radio channels provided by the reverse link 50 through the antennas16 and 18. At the central base station, the BSP 20 extracts the radiolink framing, reformatting the packet in IP form and routes it throughthe Internet gateway 22. The packet is then forwarded through any numberand/or type of TCP/IP networks, such as the Internet 24, to its ultimatedestination, such as the network file server 30.

By way of example, the wireless packet framing information may be thatdescribed in Patent Cooperation Treaty Application No. WO99/44341entitled “Dynamic Frame Size Setting For Multichannel Transmission,”published Sep. 2, 1999, and which is hereby incorporated by reference.In that scheme, Code Division Multiple Access (CDMA) encoding is used todefine multiple logical channels on a given physical channel. Forexample, a long pseudo-random noise (PN) code sequence can be used todefine multiple logical channels on a given radio frequency carriersignal. Other codes may be layered on the long PN code, such as errorcorrection codes or optional short pseudo-random noise (PN) codes, tofurther define the channels and make them robust in noisy environments.

Data may also be transmitted in the opposite direction, that is, fromthe network file server 30 to the PCs 12, in a forward direction. Inthis instance, an Internet Protocol (IP) packet originating at the fileserver 30 travels through the Internet 24 through the Internet gateway22 arriving at the BSP 20. Appropriate wireless protocol framing is thenadded to the IP packet. The packet then travels through the antenna 18and 16 to the intended receiver SAU 14. The receiving SAU 14 thenprocesses the message according to the wireless packet formatting,ultimately forwards the packet to the intended PC 12 which performs theIP layer processing. A given SAU 14 and the file server 30 are thusviewed as the end points of a given duplex connection at the IP level.Once a connection is established, a user at the PC 12 may thereforetransmit data to and receive data from the file server 30.

In accordance with the link layer or even a higher layer TCP/IPprotocol, a receiving endpoint is expected to send an acknowledgmentmessage to the corresponding sending unit upon complete and correctreceipt of a packet. This acknowledgment message may be sent in responsein a cumulative fashion, such that a given acknowledgment messageindicates that a number of consecutive packets have been receivedsuccessfully. However, in any event, it can be appreciated that theseacknowledgment messages in the system 10 must be sent over the forwardlink 40 or reverse link 50 in response to messages sent on the reverse50 or forward 40 link, respectively. Given that the system 10 is awireless system, radio resources must therefore be provisioned forsending such acknowledgment messages regardless of the exact physicallayer configuration.

As will be described in greater detail later, the reverse link 50actually consists of a number of different types of logical and/orphysical radio channels including an access channel 51, multiple trafficchannels 52-1, . . . 52-t, and a maintenance channel 53. The reverselink access channel 51 is used by the SAUs 40 to send messages torequest that traffic channels be granted to them. The assigned trafficchannels 52 then carry payload data from the SAU 14 to the BSP 20. Itshould be understood that a given IP level connection may actually havemore than one traffic channel 52 assigned to it as described in thepreviously referenced patent application. In addition, a maintenancechannel 53 may carry information such as synchronization and powercontrol messages to further support transmission of information over thereverse link 50.

Similarly, the forward link 40 typically includes a logical pagingchannel 41 that is used by the BSP 20 to not only inform the SAU 14 thatforward link traffic channels 52 have been allocated to it, but also toinform the SAU 14 of allocated traffic channels 52 in the reverse linkdirection. Traffic channels 42-1 . . . 42-t on the forward link 40 areused to carry payload information from the BSP 20 to the SAUs 14.Additionally, maintenance channels carry synchronization and powercontrol information on the forward link 40 from the base stationprocessor 20 to the SAUs 14.

Additional information as to one possible way to implement the variouslogical channels 41, 42, 43, 51, 52, and 53 is also provided in PatentCooperation Treaty Application No. WO99/63682 entitled “Fast AcquisitionOf Traffic Channels For A Highly Variable Data Rate,” published Dec. 9,1999.

As shown more particularly in FIG. 2, a typical forward link trafficchannel 42 is partitioned into a pre-determined number of periodicallyrepeating time slots 60-1, 60-2, . . . 60-n for transmission of messagesto the multiple SAUs 14. A given SAU 14 identifies messages directed toitself based upon when a message is received in an assigned time slot60. It should be understood that a given SAU 14 may at any instant intime have multiple ones of the time slots 60 assigned to it or at othertimes may have no time slots assigned to it. The assignment of timeslots 60 is communicated from a central controller such as a wirelessInternet facility base station controller 23 or the BSP 20 itself overthe paging channel 41. The allocation of radio and traffic channelsoccurs on a demand basis among the various SAUs 14 in a physical areaserviced by the system 10.

The manner of assignment of the time slots and radio channels is not ofimportance to the present invention; rather the present invention ismore concerned with the manner in which a time slot 60 is automaticallyassigned in the reverse link 50 upon reception of a valid message on theforward link 40.

In particular, the reverse link traffic channels 52 are shared among themultiple SAUs 14. For example, a given reverse link traffic channel 52-iis partitioned into a number of time slots 70-1 . . . 70-n in a mannersimilar to the way in which the forward link traffic channel 42-i ispartitioned.

Consider that a given forward link traffic channel 42-i may include aparticular time slot 60-4. This time slot 60-4 carries packet data fromthe base station processor 20 to an intended SAU 14-2. However, unlikeprior art systems, there is no specific assignment needed of reverselink traffic channel slots by sending paging channel messages to informthe connection associated with the particular time slot 60-4. Rather,upon receiving the data packet in time slot 60-4, the SAU 14 determineswhether the data has been properly received such as by performing errorcheck processing. If the packet is indicated as having been receivedproperly, the SAU 14 makes an assumption that the acknowledgment messagewill be expected to be transmitted in corresponding time slot 70-4 onthe reverse link traffic channel 52-i.

The time slot 70-4 is positioned timewise a given number of time slots,m, away from the time slot 60-4 allocated to the forward link. This, ineffect, results in automatic reservation of a reverse link time slot forthe acknowledgment message a fixed number of time slots, m, in thefuture.

Similarly, an acknowledgment message for a packet sent in time slot 60-2is acknowledged in the time slot 70-2. The time slot 70-2 remains the mtime slots away from its associated forward link time slot 60-2.

Several advantages result from this arrangement. In particular, nocontrol signaling is required on the paging channel 41 to allocatereverse link time slots for the acknowledgment messages. The techniqueefficiently uses the reverse channel for acknowledgment messages such asTCP/IP layer ARQ messages among a large number of SAUs 14. The shorttime delay duration for these acknowledgment messages in turn increasesthe effective utilization of the traffic channels 52 on the reverselink, as well as the paging channel 41 on the forward link 40.

It should be understood that the time slot 70-4 can also carry othershort messages, such as link layer acknowledgment messages. In manyapplications, link layer acknowledgments must be handled rapidly, andthe invention provides this capability.

At higher protocol levels, the reverse time slot can be used for sendingembedded links in a Web page. For example, a typical Hypertext TransferProtocol (HTTP) Web page file has several embedded links which arerequests to fetch other files. These embedded links can be sent back onthe reverse channel using the time slots 70-4.

FIG. 3 depicts a message sequence chart illustrating the transmission ofa TCP/IP packet and acknowledgment message exchange traveling in thereverse direction, that is from the PC 12 towards the server 30, withthe server 30 sending the acknowledgment message back to the PC 12. Theprotocol diagram indicates message flow from right to left through thePC 12, SAU 14, BSP 20 and Web file server 30. The protocol diagramdepicted in FIG. 3 is typical for the transmission of messages in aworldwide Web type environment.

This exchange of messages is typical of prior art systems in that achannel is explicitly allocated for acknowledgment in the messagetransmission. For example, the user of the PC 12 may be specifying a Webpage address for which it is desired to be downloaded from the fileserver 30 to the PC 12. The message thus typically consists of a higherlevel protocol (Hypertext Transfer Protocol ((HTTP), File TransferProtocol (FTP), or the like) page request or “GET” message which islayered on the TCP/IP protocol. In any event, a first message consistsof a TCP/IP layer message that contains a data packet indicated in thediagram as packet (A).

Next, the SAU 14 receives this TCP/IP layer data message 301 andreformats it for transmission over the wireless reverse link 50. Inparticular, the receipt of the TCP/IP message (A) results in a number ofmessages being sent on the access channel 51, paging channel 41, andtraffic channels 52.

First, a message 302 is sent on the access channel 51 requesting theallocation of traffic channels 52 from the BSP 20. This message 302typically consists of identification information that identifies theparticular SAU 14 requesting the traffic channels, and a command, suchas OPEN, that indicates to the BSP 20 that the associated SAU 14 isrequesting that a logical traffic channel be opened.

In response thereto, the BSP 20 sends a channel allocation message onthe forward link paging channel 41. This channel allocation message 304indicates an SAU identification (ID), and a pseudo-random noise codeassigned for the traffic channel and to permit the SAU 14 to decode itsrespective logical channel, and information indicating one or more oftime slots to which this connection is being allocated.

In response to receipt of message 304, the payload portion of the packet(A) is then partitioned by the SAU 14 among the available allocated timeslots. Thus, it may actually be necessary to transmit the packet (A) inmultiple segments indicated as SEG 1, SEG 2, . . . SEG p in multipletraffic messages 306, 308, . . . , 312 sent on the traffic channels 52.It should be understood that depending on system loading requirementsand capacity, a given connection may be allocated a single time slot ona single reverse link traffic channel 52, or it may be the situationwhere multiple traffic channels and/or time slots may be allocated totransmission of the various segments of packet (A).

In any event, the BSP 20 receives the messages 306, 308, . . . , 312containing the various segments SEG 1, SEG 2, . . . SEG p andreassembles them into the complete TCP/IP data packet (A). The assembledpacket (A) is then reformulated as a TCP/IP message 314 and forwarded tothe Web file server 30.

If Web file server 30 receives packet (A) correctly, it then provides anacknowledgment message 316 intended for the PC 12 that originated themessage. To send this acknowledgment message thus requires theallocation of a radio channel to forward it to the respective SAU 14.This channel allocation process involves first sending a message 317 onthe forward paging channel 41 indicating to the respective SAU toallocate a code channel and time slot for the acknowledgment message.

A message 318 is then sent on the indicated traffic channel with theappropriate code and assigned time slot for the acknowledgment 318. Uponreceipt of message 318 at the SAU 14, the acknowledgment message isreformulated as a TCP/IP level frame in message 320 and forwarded to thePC 12. Further messages are then needed to de-allocate the forward linktraffic channel 40 allocated for the acknowledgment message by, forexample, sending a message 322 on the access channel requesting that thetraffic channel be closed, and acknowledgment of the closing of themessage being returned on the paging channel by message 324.

Turning attention now to FIG. 4, it can be understood how messages areexchanged for acknowledgment on the forward link 40 without the need toexplicitly allocate channels for acknowledgment messages on the reverselink 50. FIG. 4 depicts the message sequence for a packet (B) travelingin a forward link 40 direction from the Web server 30 towards the PC 12.It will be understood in this situation that these packets typicallyinclude Web page data being transmitted down to the PC 12 from the Webfile server 30, and thus are typically transmitted far more often thanmessages traveling in the reverse link 50 direction. Thus, these forwardlink messages, being far more common and prevalent, benefit greatly froma more efficient acknowledgment scheme.

In any event, the data packet (B) originates as a TCP/IP level message400 at the Web server 30 and is then forwarded to the BSP 20. Uponreceipt of this message 400, the BSP 20 then causes a number of messages412, 414, 416 and 418 to be exchanged between the BSP 20 and SAU 14. Inparticular, a paging channel message 412 is sent on the forward link 40indicating an SAU ID, PN code, and one or more time slots being assignedbetween the BSP 20 and the particular SAU 14. This message is thenacknowledged, for the wireless physical layer connection, by a returnmessage 414 being sent from the SAU 14 back to the BSP 20. Thisindicates to the BSP 20 that the SAU 14 is ready to receive data.

The BSP 20 then proceeds to send the various segments SEG. 1, SEG. 2, .. . SEG. s as a series of messages 416, 417, 418 sent on one or more ofthe forward traffic channels 42 at indicated slots and with indicatedcodes. Upon completion of these messages, SAU 14 has received all of thesegments making up the packet (B). These segments may then bereformulated as a TCP/IP layer data packet (B) in a message 420 which isforwarded to the PC 12.

The PC 12 then returns an acknowledgment message 422 to the SAU 14. Thisin turn causes a single message 424 to be sent on a traffic channel onthe reverse link 50. The time slot for this message is determined fromthe time slots allocated on the forward link to the same connection.(This has been described previously in connection with FIG. 2.) Theacknowledgment message is received at the BSP 20 and then reformulatedas a TCP/IP layer acknowledgment packet 430 and forwarded to the Webserver 30.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A method for communication comprising: receiving a forward linkmessage on a forward link channel in an allocated first time intervalincluding at least one time slot; transmitting on a reverse link channelreverse link message in response to the forward link message in a secondtime interval including at least one time slot, wherein the second timeinterval on the reverse link is positioned a predetermined time periodaway from the first time interval allocated on the forward link channel,wherein the second time interval is positioned without receiving aspecific time interval allocation message.
 2. The method of claim 1wherein the reverse link message is an acknowledgment message for theforward link message.
 3. The method of claim 1 wherein the reverse linkmessage is a TCP/IP layer acknowledgment message for the forward linkmessage.
 4. The method of claim 1 wherein the reverse link message is anHTTP layer embedded link request.
 5. The method of claim 1 wherein theforward link message is a network layer packet.
 6. An apparatuscomprising: a receiving component configured to receive forward linkmessage on a forward link channel in an allocated first time intervalincluding at least one time slot; a transmitting component configured totransmit on a reverse link channel a reverse link message in response tothe forward link message in a second time interval including at leastone time slot, wherein the second time interval on the reverse link ispositioned a predetermined time period away from the first time intervalallocated on the forward link channel, wherein the second time intervalis positioned without receiving a specific time interval allocationmessage.
 7. The apparatus of claim 6, wherein the reverse link messageis an acknowledgment message for the forward link message.
 8. Theapparatus of claim 6, wherein the reverse link message is a TCP/IP layeracknowledgment message for the forward link message.
 9. The apparatus ofclaim 6, wherein the reverse link message is an HTTP layer embedded linkrequest.
 10. The apparatus of claim 6, wherein the forward link messageis a network layer packet.
 11. A code division multiple access (CDMA)subscriber unit comprising: circuitry configured to receive a firstmessage in an allocated first time interval, wherein the first timeinterval includes at least one time slot; and circuitry configured, inresponse to receipt of the first message, to transmit an acknowledgementin a second time interval of a reverse link, wherein the second timeinterval is a predetermined time period after the first time intervaland a specific allocation of the second time interval is not received bythe CDMA subscriber unit.
 12. The CDMA subscriber unit of claim 11,wherein the first message is received over a plurality of code channels.13. The CDMA subscriber unit of claim 11, wherein the acknowledgment istransmitted over a code channel.
 14. The CD1VIA subscriber unit of claim11, wherein the acknowledgement is transmitted in response to anautomatic repeat request mechanism.
 15. The CD1VIA subscriber unit ofclaim 11 further comprising circuitry configured to transmit a codechannel in addition to the acknowledgment, wherein the additional codechannel includes power control information.
 16. The CDMA subscriber unitof claim 15, wherein the additional code channel includes signalinginformation.
 17. The CDMA subscriber unit of claim 11, wherein the firstmessage includes packet data.